An illumination optical unit of the type mentioned in the introduction is known from US 2011/0001947 A1, WO 2009/132 756 A1, WO 2009/100 856 A1 and from U.S. Pat. No. 6,438,199 B1 and U.S. Pat. No. 6,658,084 B2. A field facet mirror is known from DE 19 931 848 A1, from WO 2008/149 178 A1, from DE 10 2011 076 145 A1 and from U.S. Pat. No. 6,859,328.